CN110726362A - Displacement measuring device, error temperature compensation system and method - Google Patents

Abstract

The invention discloses a displacement measuring device, comprising a sliding scale, a sliding guide rail, a reference target ball, a fixed base, a magnet and a spring; discloses an industrial robot end positioning error temperature compensation system, including a displacement measuring device and an industrial robot Robots, computers, racks, communication cables, data acquisition cards. A temperature compensation method for the positioning error of the end of an industrial robot is disclosed for obtaining a compensated kinematic model. The displacement measuring device in the present invention can be effectively connected with the industrial robot and the external data acquisition card, and the industrial robot end positioning error temperature compensation system constructed through the connection can effectively collect the actual displacement measured by the displacement measuring device and transmit it to the computer, and The compensation method of the present invention is further integrated to construct a compensated kinematic model, so as to calculate the end coordinates after compensation, realize temperature error compensation of the industrial robot, and improve its positioning accuracy.

Description

Displacement measuring device, error temperature compensation system and method

technical field

The invention relates to a displacement measuring device, an error temperature compensation system and a method, and belongs to the field of robots.

Background technique

Industrial robots are a key part of industrial automation and intelligent manufacturing, and an important step in the transformation and upgrading of traditional manufacturing. And the requirement of its positioning accuracy is also increasing day by day. At present, most of the industrial robots used in factories are programmed in the teaching mode, which is inefficient. At the same time, this mode mostly depends on the repeatability of the robot. In arc welding, laser cutting and other operations, the robot not only requires high repeatability, but also high absolute positioning accuracy.

The repetition accuracy of industrial robots can often reach the order of 0.1, while the absolute positioning accuracy is often low, usually in the order of 1mm. In practical applications, most of the absolute positioning errors are caused by the inconsistency between its own kinematic parameters and the nominal kinematic parameters in the controller. Temperature change is an important factor affecting the absolute positioning accuracy of the robot, because temperature changes will cause the robot connecting rods and joints to elongate and shorten, and it is of practical significance to compensate for the absolute positioning error caused by temperature changes. models, and lack of applicable metrics to compensate.

SUMMARY OF THE INVENTION

The invention provides a displacement measuring device for constructing a platform connected with an industrial robot and an external acquisition device, and provides a temperature compensation system for the positioning error of the end of an industrial robot, so as to realize the connection with the displacement measuring device, and is used for The data of the displacement measuring device is collected, and then a platform for temperature compensation of the end positioning error of an industrial robot is provided; a temperature compensation method of the end positioning error of an industrial robot is provided, so as to obtain a compensated kinematic model according to the obtained data.

The technical scheme of the present invention is: a displacement measuring device, comprising a sliding scale 4, a sliding guide rail 8, a reference target ball 10, a fixed base 11, a magnet 15, and a spring 16;

A magnet 15 is installed in the tapered hole of the fixing base 11, and the reference target ball 10 is fixed in the tapered hole by the magnet; one end of the sliding guide rail 8 is connected with the reference target ball 10; the starting position of the chute in the sliding guide rail 8 is fixed with a spring One end of 16, the other end of the spring 16 is fixed on one end of the sliding scale 4, and the sliding scale 4 is installed in the chute; the bottom surface of the sliding groove of the sliding guide 8 is installed with a fixed grid, and the sliding scale 4 is installed on the side that is in contact with the bottom surface of the sliding guide 8. There is a moving grille.

The sliding scale 4 is made of carbon fiber.

An anti-falling frame 13 is installed on the outer surface of the sliding guide rail 8 to prevent the sliding scale 4 from deviating from the chute.

An industrial robot end positioning error temperature compensation system, comprising a displacement measurement device, an industrial robot 1, a computer 2, a frame 3, a communication cable 6, and a data acquisition card 7;

The fixed base 11 is installed on the rack 3 by screws II 12; the other end of the sliding scale 4 is provided with a cross-shaped adapter plate 9, which is matched with the through holes of the cross-shaped adapter plate 9 through the screws I5, and the sliding scale 4 is connected to. On the flange at the end of the robot 1; the computer 2 is connected to the data acquisition card 7 through the communication cable 6, and the data acquisition card 7 is connected to the displacement measuring device and the controller 14 of the robot 1 through the communication cable 6.

A method for temperature compensation of end positioning error of an industrial robot, the specific steps of the method are as follows:

Step 1. Install the industrial robot end positioning error temperature compensation system;

Step 2. Power on, the robot 1 moves along T points in the workspace; the initial point and all other command points need to be located in the workspace;

Step 3. Under the current working temperature of robot 1, when the center point of the end of robot 1 moves along the T points in the workspace, the displacement measuring device will move with the end of robot 1, and the t-1th point to The command displacement of the t-th point under the motion command is dc _(t-1,t) , t=1,2,...T; at each command position, record the distance from the center point of the end of the robot 1 to the center of the reference target ball 10 distance, and record the coordinates of the center point of the end of the robot 1 in the robot coordinate system; the connection line between two adjacent points in space and the center of the reference target ball 10 of the displacement measuring device forms a triangle, through the geometric relationship of the triangle, The coordinates of two adjacent points in the space and the distance from these two points to the center of the reference target ball 10 of the displacement measuring device, and the displacement between the two adjacent points is calculated and recorded as the actual displacement dr _(t-1,t) , once A total of T displacement data can be collected in the cycle; the distance from the center point of the end of the robot 1 to the center of the reference target ball 10 is read by the data acquisition card 7, and the coordinates of the center point of the robot end in the robot coordinate system are read by the data acquisition card. 7 read from the robot controller 14;

Step 4. According to the accumulation and average of the ratio of the actual displacement dr _{(t-1, t)} and the command displacement dc _{(t-1, t)} between all adjacent points collected in this cycle to obtain this cycle The proportional coefficient K _m of the end displacement of the robot affected by temperature is calculated as follows:

Among them, m represents the mth cycle;

Step 5. Repeat steps 3 and 4 for a total of N times. Using the proportional coefficient K _m of the end displacement change of each cycle, m=1...N, and taking the average value of K _m as the correction coefficient, it can be calculated that the robot 1 is working. The proportional coefficient K of the overall terminal displacement change affected by temperature in the field is calculated as follows:

Step 6. According to the principle of robot kinematics, the transformation matrix ^n-1 A _n from the n-1th joint to the nth joint based on the Denavit-Hartenberg model is:

Among them, θ _n is the joint rotation angle of the n-th joint, d _n is the joint length of the n-th joint, α _n is the connecting rod twist angle of the _n -th joint, and an is the rod length of the n-th joint; A _rz (θ _n ) represents the rotation about the Z-axis of the nth joint by θ _n degrees, A _tz (d _n ) represents the length of the translation d _n along the Z-axis of the nth joint, and A _tx (a _n ) represents the length along the nth joint’s Z axis The length of the X-axis translation an _n of the joints, _Arx (α _n ) represents the rotation of α _n degrees around the X-axis direction of the nth joint, then the total kinematics model of the six-degree-of-freedom robot can be expressed as:

Step 7. Use K to calculate the actual joint length _dn ' and member _length an':

d _n '=K·d _n

_an '=K· _an ;

Step 8. Substitute the actual joint length _dn ' and the rod _length an' corrected by the coefficient K into the overall kinematics model of the robot to obtain a compensated kinematics model.

The beneficial effects of the present invention are: the displacement measuring device in the present invention can be effectively connected with the industrial robot and an external data acquisition card, and the industrial robot end positioning error temperature compensation system constructed through the connection can effectively collect the data measured by the displacement measuring device. The actual displacement is transmitted to the computer, and the compensation method of the present invention is further integrated to construct a compensated kinematic model, so as to calculate the compensated end coordinates, realize temperature error compensation of the industrial robot, and improve its positioning accuracy.

Description of drawings

Fig. 1 is the industrial robot end positioning error compensation system in the present invention;

Fig. 2 is the schematic diagram of displacement measuring device in the present invention;

Fig. 3 is the schematic diagram of sliding scale among the present invention;

Fig. 4 is the schematic diagram of the sliding guide rail after being connected with target ball in the present invention;

Fig. 5 is the flow chart of the terminal positioning error compensation method in the present invention;

The labels in the figure are: 1-industrial robot, 2-computer, 3-frame, 4-slide ruler, 5-screw I, 6-communication cable, 7-data acquisition card, 8-slide guide, 9-ten Font-shaped adaptation plate, 10-reference target ball, 11-fixed base, 12-screw II, 13-anti-falling frame, 14-controller, 15-magnet, 16-spring, 17-fixed grid.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and embodiments, but the content of the present invention is not limited to the scope.

Embodiment 1: As shown in Figures 1-5, a displacement measurement device includes a sliding scale 4, a sliding guide rail 8, a reference target ball 10, a fixed base 11, a magnet 15, and a spring 16;

A magnet 15 is installed in the tapered hole of the fixed base 11, and the reference target ball 10 is fixed in the tapered hole by the magnet; one end of the sliding guide 8 is connected with the reference target ball 10 by welding; the starting position of the chute in the sliding guide 8 One end of the spring 16 is fixed, and the other end of the spring 16 is fixed at one end of the sliding scale 4. The sliding scale 4 is installed in the chute, and the mechanical cooperation relationship between the two sides of the sliding scale 4 that is not in contact with the bottom surface of the chute and the surface of the chute is directly carried out. Fastening; a fixed grid is installed on the bottom surface of the chute of the sliding guide rail 8, and a moving grid is installed on the side of the sliding scale 4 in contact with the bottom surface of the sliding groove of the sliding guide rail 8.

The capacitance between the moving grid and the fixed grid changes correspondingly with the relative displacement between the two. At the same time, the change of the capacitance will affect the AC signal. A fixed frequency AC signal is given to the moving grid through the data acquisition card 7: such as 3.3V AC voltage signal, by analyzing the change of the AC signal, the specific value of the capacitance change can be obtained, so as to calculate the displacement of the sliding scale 4, and finally obtain the distance from the center point of the end of the robot 1 to the center of the reference target ball 10. The data acquisition card 7 may be an embedded device based on a TMS320F280040C microprocessor.

The spring 16 has a certain amount of initial deformation, so that the sliding scale 4 reciprocates stably in the sliding guide 8 during the whole measurement process; meanwhile, the sliding guide 8 can rotate around the tapered hole and has multiple degrees of freedom.

Further, the material of the sliding scale 4 can be set to be carbon fiber material, and since the material is very little affected by temperature, its measurement accuracy will not change with temperature.

Further, an anti-falling frame 13 may be installed on the outer surface of the sliding guide rail 8 to prevent the sliding scale 4 from deviating from the chute.

An industrial robot end positioning error temperature compensation system, comprising a displacement measurement device, an industrial robot 1, a computer 2, a frame 3, a communication cable 6, and a data acquisition card 7;

The fixed base 11 is installed on the rack 3 by screws II 12; the other end of the sliding scale 4 is provided with a cross-shaped adapter plate 9, which is matched with the through holes of the cross-shaped adapter plate 9 through the screws I5, and the sliding scale 4 is connected to. On the flange at the end of the robot 1; the computer 2 is connected to the data acquisition card 7 through the communication cable 6, and the data acquisition card 7 is connected to the transmitting electrode of the moving grid of the sliding scale 4 and the controller 14 of the robot 1 through the communication cable 6. The data acquisition card 7 transmits the collected actual displacement measured by the displacement measuring device to the computer 2 .

A method for temperature compensation of end positioning error of an industrial robot, the specific steps of the method are as follows:

Step 1. Install the industrial robot end positioning error temperature compensation system;

Step 2. Power on, the robot 1 moves along T points in the workspace; the initial point and all other command points need to be located in the workspace;

Step 3. Under the current working temperature of robot 1, when the center point of the end of robot 1 moves along the T points in the workspace, the displacement measuring device will move with the end of robot 1, and the t-1th point to The command displacement of the t-th point under the motion command is dc _(t-1,t) , t=1,2,...T; at each command position, record the distance from the center point of the end of the robot 1 to the center of the reference target ball 10 distance, and record the coordinates of the center point of the end of the robot 1 in the robot coordinate system; the connection line between two adjacent points in space and the center of the reference target ball 10 of the displacement measuring device forms a triangle, through the geometric relationship of the triangle, The coordinates of two adjacent points in the space and the distance from these two points to the center of the reference target ball 10 of the displacement measuring device, and the displacement between the two adjacent points is calculated and recorded as the actual displacement dr _(t-1,t) , once A total of T displacement data can be collected in the cycle; the distance from the center point of the end of the robot 1 to the center of the reference target ball 10 is read by the data acquisition card 7, and the coordinates of the center point of the robot end in the robot coordinate system are read by the data acquisition card. 7 read from the robot controller 14;

Step 4. According to the accumulation and average of the ratio of the actual displacement dr _{(t-1, t)} and the command displacement dc _{(t-1, t)} between all adjacent points collected in this cycle to obtain this cycle The proportional coefficient K _m of the end displacement of the robot affected by temperature is calculated as follows:

Among them, m represents the mth cycle;

Step 5. In order to reduce the random error in the measurement, repeat steps 3 and 4 for a total of N times, use the proportional coefficient K _m of the end displacement change of each cycle, m=1...N, and take the average value of K _m as the correction coefficient , the proportional coefficient K of the overall end displacement of robot 1 affected by temperature in the work site can be calculated. The calculation formula is as follows:

Step 6. According to the principle of robot kinematics, the transformation matrix ^n-1 A _n from the n-1th joint to the nth joint based on the Denavit-Hartenberg model is:

Among them, θ _n is the joint rotation angle of the n-th joint, d _n is the joint length of the n-th joint, α _n is the connecting rod twist angle of the _n -th joint, and an is the rod length of the n-th joint; A _rz (θ _n ) represents the rotation about the Z-axis of the nth joint by θ _n degrees, A _tz (d _n ) represents the length of the translation d _n along the Z-axis of the nth joint, and A _tx (a _n ) represents the length along the nth joint’s Z axis The length of the X-axis translation an _n of the joints, _Arx (α _n ) represents the rotation of α _n degrees around the X-axis direction of the nth joint, then the total kinematics model of the six-degree-of-freedom robot can be expressed as:

Step 7. Use K to calculate the actual joint length _dn ' and member _length an':

d _n '=K·d _n

_an '=K· _an ;

Through experiments and theoretical analysis, it is obtained that the proportional coefficient K _is equal to the variation coefficient of the joint length d _n of the robot 1 and the rod length an . Therefore, K can be used to calculate the actual joint length d _n ' and the rod _length an ' .

Step 8. Substitute the actual joint length _dn ' and the rod _length an' corrected by the coefficient K into the overall kinematics model of the robot to obtain a compensated kinematics model. According to the robot kinematics model, the compensated end coordinates can be calculated, so as to realize the temperature error compensation of the industrial robot and improve its positioning accuracy.

The standard robot kinematics model includes four sets of parameters, including two sets of linear parameters: joint length and rod length, and two sets of angular parameters: joint rotation angle and link rotation angle. Through creative labor, the present invention selects two sets of parameters, the joint length and the rod length, and removes the joint rotation angle and the connecting rod torsion angle, which have very limited influence. By using the system and method to measure the commanded displacement of the industrial robot at the current working temperature, the change rate of the robot end displacement is calculated. The error of the joint length and rod length of the industrial robot caused by temperature further compensates for the positioning error of the robot end caused by temperature.

The invention has the characteristics of simple structure, easy operation, system modularization and integration. This method does not need to switch the robot to the hot and cold states for measurement, avoids the additional measurement error and cost caused by using temperature sensors, can quickly and easily compensate for the positioning error of the end of the industrial robot caused by temperature changes, and the entire system is compact It is convenient and has low requirements for the external environment, and can be flexibly adapted to the work of the industrial site.

The specific embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned embodiments, and can also be made within the scope of knowledge possessed by those of ordinary skill in the art without departing from the purpose of the present invention. Various changes.

Claims (5)

1. A displacement measuring device, characterized by: comprises a sliding scale (4), a sliding guide rail (8), a reference target ball (10), a fixed base (11), a magnet (15) and a spring (16);

a magnet (15) is arranged in a taper hole of the fixed base (11), and the reference target ball (10) is fixed in the taper hole through the magnet (15); one end of the sliding guide rail (8) is connected with a reference target ball (10); one end of a spring (16) is fixed at the initial position of a sliding groove in the sliding guide rail (8), the other end of the spring (16) is fixed at one end of a sliding scale (4), and the sliding scale (4) is arranged in the sliding groove; the bottom surface of the sliding chute of the sliding guide rail (8) is provided with a fixed grid, and the surface of the sliding scale (4) contacted with the bottom surface of the sliding chute of the sliding guide rail (8) is provided with a movable grid.

2. The displacement measuring device according to claim 1, characterized in that: the sliding scale (4) is made of carbon fiber materials.

3. The displacement measuring device according to claim 1, characterized in that: and the outer side surface of the sliding guide rail (8) is provided with an anti-falling frame (13) to prevent the sliding scale (4) from deviating from the sliding groove.

4. The utility model provides an industrial robot end positioning error temperature compensation system which characterized in that: a displacement measuring device according to any of claims 1-3, further comprising an industrial robot (1), a computer (2), a frame (3), a communication cable (6), a data acquisition card (7);

the fixed base (11) is arranged on the rack (3) through a screw II (12); the other end of the sliding scale (4) is provided with a cross-shaped adapting flat plate (9), and the sliding scale (4) is connected to a flange at the tail end of the robot (1) through the matching of a screw I (5) and a through hole of the cross-shaped adapting flat plate (9); the computer (2) is connected with the data acquisition card (7) through the communication cable (6), and the data acquisition card (7) is connected with the transmitting electrode of the moving grid of the sliding scale (4) and the controller (14) of the robot (1) through the communication cable (6).

5. A temperature compensation method for end positioning errors of an industrial robot is characterized by comprising the following steps: the method comprises the following specific steps:

step 1, installing the industrial robot end positioning error temperature compensation system of claim 4;

step 2, electrifying, wherein the robot (1) moves along T points in the working space; wherein the initial point and all other instruction points need to be located in the workspace;

and 3, when the central point of the tail end of the robot (1) moves along T points in the working space at the current working temperature of the robot (1), the displacement measuring device moves along with the tail end of the robot (1), and the command displacement from the T-1 point to the T point under the motion command is dc_(t-1,t)T is 1,2, … T; recording the distance from the central point of the tail end of the robot (1) to the sphere center of the reference target sphere (10) at each instruction position, and recording the coordinates of the central point of the tail end of the robot (1) in a robot coordinate system; of two points adjacent in space with the centre of the reference target ball (10) of the displacement measuring deviceThe connecting lines form a triangle, and the displacement between two adjacent points is calculated by the geometric relationship of the triangle, the coordinates of the two adjacent points in the space and the distance between the two points and the sphere center of the reference target ball (10) of the displacement measuring device and is recorded as the actual displacement dr_(t-1,t)T displacement data can be acquired in one cycle; the distance from the central point of the tail end of the robot (1) to the sphere center of the reference target ball (10) is read through a data acquisition card (7), and the coordinate of the central point of the tail end of the robot in a robot coordinate system is read from a robot controller (14) through the data acquisition card (7);

step 4, according to the actual displacement dr between all the collected adjacent points in the cycle_(t-1,t)With a command displacement dc_(t-1,t)The ratio is accumulated and averaged to obtain the tail end displacement change proportionality coefficient K of the robot in the current cycle, which is influenced by the temperature_mThe calculation formula is as follows:

wherein m represents the mth cycle;

step 5, repeating the step 3 and the step 4 for N times, and using the tail end displacement change proportionality coefficient K of each circulation_mM is 1 … N and K is taken_mThe average value of the total displacement change ratio coefficient K is used as a correction coefficient, the total displacement change ratio coefficient K of the robot (1) influenced by the temperature in a working site can be calculated, and the calculation formula is as follows:

step 6, according to the kinematics principle of the robot, a matrix is transformed from the (n-1) th joint to the (n) th joint based on the Denavit-Hartenberg model^n-1A_nComprises the following steps:

wherein, theta_nIs the joint angle of the nth joint, d_nIs as followsJoint length of n joints, alpha_nIs the link torsion angle of the nth joint, a_nThe length of the rod piece of the nth joint; a. the_rz(θ_n) Representing rotation theta about the Z-axis of the nth joint_nDegree, A_tz(d_n) Representing a translation d along the Z-axis of the nth joint_nLength of (A)_tx(a_n) Representing a translation a in the X-axis direction of the nth joint_nLength of (A)_rx(α_n) Indicating a rotation alpha in the X-axis direction about the nth joint_nDegree, then the total kinematic model of the robot in six degrees of freedom can be expressed as:

step 7, calculating the actual joint length d by using K_n' and rod length a_n'：

d_n'＝K·d_n

a_n'＝K·a_n；

Step 8, correcting the actual joint length d after the coefficient K_n' and rod length a_nAnd substituting the motion data into the robot total kinematic model to obtain a compensated kinematic model.

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